1) Field of the Invention
The invention is related to communication networks, and in particular, to network control systems and methods.
2. Description of the Prior Art
The advancement of the Internet has influenced the telecommunications industry to develop Internet Protocol (IP) based services. IP provides a flexible framework to support services from simple file transfer and electronic mail to more complex services like Internet-based gaming and Internet telephony. Voice-over IP (VoIP) services have been available since the inception of the Internet but have lacked quality of service (QoS) mechanisms. Network traffic and congestion cause voice quality to vary from toll grade to satellite quality or worse. As the Internet has matured, consumer demand for integrated IP service offerings has grown. This demand for integrated services has forced telecom providers to address issues such as network congestion and low QoS.
The telecommunications industry has addressed these issues by, for example, over engineering IP backbones to mitigate IP congestion and transporting IP traffic over Asynchronous Transfer Mode (ATM) networks to provide high QoS. Additional solutions developed to address these issues include implementing Telephone Routing over Internet Protocol (TRIP) and Session Initiation Protocol (SIP). TRIP is a telephony routing protocol developed to provide an IP network with next hop routing information for call requests. TRIP is designed to operate independently of signaling protocols. This allows network designers to implement TRIP in varied network environments. Session Initiation Protocol (SIP) is an underlying signaling protocol for networks utilizing TRIP.
Internet systems route communications over the Internet by packaging the communications within data packets and transporting the packets according to routing instructions contained in the packets. Routing voice communications over the Internet occurs in a similar manner. A typical internet telephony system that includes an originating telephone and a destination telephone both connected to the Internet can route packets carrying communications without leaving the Internet. However, to bridge Internet telephony calls originating on the Internet to destinations located off the Internet (such as a telephone connected to the public switched telephone network) requires media gateways to interface between the origin and the destination.
To effectively interface between Internet telephony systems and the PSTN, media gateways must be strategically located. Various systems within the Internet systems must be aware of the locations of the media gateways and the status of each individual gateway. In particular, location servers share responsibility for knowing the location and status of each gateway, and for initiating telephony sessions across the gateways utilizing the Session Initiation Protocol (SIP). SIP uses client-server interaction, with servers being divided into two types. A user runs a soft client on, for example, a SIP phone. It is assigned an identifier (e.g. SIPuser@domain.com) and can receive incoming calls. The second type of server is intermediate (i.e. sits between two SIP phones) and handles tasks such as call set up, call forwarding and call redirects. The intermediate server is called a SIP Proxy server. The location server is an entity built into the Proxy server. In a basic SIP network, the proxy server can forward an incoming call request to the next proxy server along the path to the called phone. It also can provide information back to a caller to provide destination information so that the caller can reach the destination SIP phone directly.
The location servers are running on SIP proxies Telephony Routing over Internet Protocol (TRIP) enabled. TRIP is a protocol established to effectuate messaging between location servers and gateways to keep track of the location and status of the gateways. TRIP does not run directly over IP. It must ride over a telephony protocol like SIP or H.323. IP does not provide the infrastructure (e.g. SIP proxy server and media gateway) nor the packet structure to provide what TRIP needs to do its very specific job (dynamic building of proxy server routing tables). The location server is a software entity of a SIP proxy. In a SIP only network the LS is not used—the SIP proxy will use DNS (Domain Name Service) to look up where to forward call requests. In a TRIP enabled SIP network, the location server uses update messages from media gateways and other location servers to build a dynamic routing table that the SIP proxy uses to forward and redirect call requests.
FIG. 1 illustrates media gateway system 100 in the prior art. Media gateway system 100 includes location server 110, gateway 120, and PSTN 130. Gateway 120 is in communication with TRIP enabled location server 110 by SIP messaging, and in communication with PSTN 130 by signaling system 7 (SS7) messaging or some other similar messaging protocol. In the prior art, gateway 120 is TRIP-lite enabled a SIP proxy runs TRIP enabled location server 110. When the status of gateway 120 changes, gateway 120 transmits TRIP-lite update messages to location server 110 indicating the status change. Location server 110 can then send TRIP messages to other TRIP enabled location servers to update the other location servers on the status of gateway 120. Currently, TRIP enabled systems utilize transport control protocol (TCP) for the transport of TRIP messaging.
TRIP-enabled entities running within a SIP environment utilize reliable intra-flooding update messaging mechanisms modeled after the Open Shortest Path First linked state protocol to locate optimum paths for session instantiation. However, the OSPF model lacks the ability to efficiently select IP telephony routes. Furthermore, the OSPF model lacks scalability characteristics desired for IP telephony.